Method of removing acetylenes from diolefin mixtures



.Aug. 28', 1951 C. E. MORRELL METHOD OF REMOVING ACETYLENES FROM DIOLEFIN MIXTURES Filed Nov. 6. 1943 2 Sheets-Sheet 2 PARA 7'0v f GIL 3:203:52

'SORKIR Patented Aug. 28, 1951 METHOD OF REMOVING ACETYLEN ES FROM DIOLEFIN MIXTURES Charles E. Morrell,"Westfield, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application November 6, 1943, Serial No. 509,168

3 Claims. (01. 2s0' ss1.5)

This lnventionrelates to improvements in the extraction of diolefins and relates particularly to improvements in the separation of diolefins from mixtures of hydrocarbons containing diolefins and acetylenes by the use of copper salt solutions.

It is known that ammoniacal cuprous acetate solutions of appropriate composition are capable of extracting 'diolefins for example butadiene, though other diolefins such as isoprene, piperylene and dimethyl butadiene may be similarly extracted from hydrocarbon mixtures such as those obtained by thermal cracking of oil, and by catalytic dehydrogenation of butenes and butanes, yielding as a product butadiene of extremely high purity. It has been found that unsaturated hydrocarbons other than butadiene are also absorbed by the solution when contacted therewith. Among such hydrocarbons are the butenes, the acetylenes and the allenes. The acetylenes of most interest in processes for concentrating butadiene are methyl acetylene, ethyl acetylene and vinyl acetylene. The copper solutions described have quite high dissolving power for the acetylenes. For instance, in the case of a hydrocarbon gas containing 0.1% of any of the'acetylenes designated, a copper solution brought to equilibrium therewith at 100 F. contains about 0.19 mol of dissolved acetylenes per liter of solution or about 0.8% by .weight. Higher concentrations of acetylenes in the gas phase result in higher concentrations of acetylene dissolved in the solution. It is not feasible or desirable to increase the dissolved acetylenes content of these solutions to too high a level since under such conditions precipitation of solid copper acetylides is encountered. The presence of these solids in an operating system is undesirable since they tend to stop the flow of liquid and since they constitute a hazard due to their tendency to decompose with some violence under proper activation. One means for preventing these difliculties is a regulation of the copper solution composition and, more specifically, the use of ammonia in excess of that required to solubilize the cuprous oxide dissolved in the solution.

Although cuprous acetate solutions of appropriate composition are capable of dissolving appreciable amounts of such acetylenes without precipitating copper acetylides, it is necessary to remove these acetylenes from the solution in any process in which the solution is continually recycled through the butadiene extraction system. Part of these dissolved acetylenes can be removed along with the butadiene product in the step in 2 which the dissolved butadiene is boiled out of the'solution. Acetylenes such as vinyl acetylene and ethyl acetylene however are undesirable in the product butadiene and hence only limited amounts can be removed from the solution in thisrnanner. Another method for removing the dissolved acetylenes is to boil them out of the copper solution together with ammoniain a step subsequent to the one in which butadiene is boiled out of the solution. Still another method for efiecting acetylenes removal consists of heating the solution for an appropriate period of time at temperatures in the range of ISO-200 F. subsequent to the removal of butadiene in the desorption step of a cyclic process. In such a heating step acetylenes such as ethyl acetylene, vinyl acetylene, methyl acetylene (hereafter designated as monomeric acetylenes) are polymerized to higher boiling materials. This is described in our co-pending application, Serial No. 453,544, filed August 4, 1942, of which the present application is a continuation-in-part. It has been found that the initial step in such a polymerization reaction consists of formation of dimers in the case of pure acetylenes and of codimers in the case of mixed acetylenes. If butadiene and allenes are present copolymers of the acetylenes and these hydrocarbons are also formed. Some polymerization of the butadiene and allenes likewise results. These resulting dimeric materials are considerably less soluble in the copper solution than are the monomeric acetylenes from which'they are derived. Under prolonged heating conditions, however, the dimers and codimers formed in this manner continue to polymerize giving rise to materials of higher molecular weight which in many instances may be insoluble in'all common solvents. The nature of these higher molecular weight polymers depends to a considerable extent upon the following factors:

been found that if the dimers are dissolved in a solvent such as a hydrocarbon in which they are miscible and allowed to polymerize in such a'medium the nature of the resulting high molecular, weight materials is different from the nature of the materials obtained when no added hydrocarbon solvent is present. For instance, if

the dimers are dissolved in a highly aromatic enes and other polymers from the absorbent:

copper solutions in a cyclic process for concentrating butadiene and otherolefins; This object; is accomplished by removing these polymers from the solution by contacting thelatterwith ailiquid which is not appreciably miscible withithe coppere solution and which is capable of dissolving considerable amounts of both the acetylene polymflrs.

and other polymers from the latter; Such solvents include hydrocarbon fractions of: a: wide:

range of boiling points,j}nore specifically, those boiling from the C4 range through. the; gas-oil range. Theymay consist of parafiina paphthenes olefins and aromatics or. mixturesof these, althoughfractions relatively. high inclei ns and/or aromatics are preferred. 1 For example, the solvent. may. be composed of butenes Other solventswhich are efiective for-this purposeare higheralcohols, that is, alcohols containing more than carbon atoms, ketones containing more than. 5 or 6 carbonv atoms and other oxygenated materials which-are of .limitedfsolubility int-he copper solution. and which do not react-chemicallywith thesolution. The latter areoj; limited applicability, howev.er,. due. to, their, relatiyely high cost and? for this-reason weprefer to, use hydrocarbon, materials The solubility of the polymers. in hydrocarbon fractions varies with -the.natur.e ofthe. fraction and with the. molecular." weight of the polymer.

PolymersI of higher molecular weight. are less soluble than those of lower:molecular'weight, Ethyl acetylene and meth-yl acetylene by themselves. andin mix tures ;with; each othendonot exhibit tendenciesto form. polymers ofsufliciently high molecular'weight that marked insolnbility of-the;resulting polymers in hydrocarbons-of a wide range of compositionsand boiling-points is manifested. In the case-of; vinyl acetylene hpw ever, and ofs-mixtures of vinyl acetylenesrwith other acetylenes, polymers .ofsufiiciently; high molecular weights are obtained so that; they are not completely soluble even in-"thecaseof sole vents of high dissolving power suchas-aromatic fractions; l-lowever even in the case. of;these polymers which are not completely soluble-in hydrocarbons it has been; discovered that these polymers are effectively separated from thefsolur tion, in which they are. in suspensiom-by washing the solution with a hydrocarbon. While;this-ac tion-undoubtedlyv is in'. part one'of solution of. the polymer there is also involved a, wettingr'of the undissolved polymer by the oilto such a degree that it is preferentially retained, by the hydrocarbon rather than by thecopper-solution.- In such cases, it is observedthat the portion .of the polymers insoluble in; the hydrocarbon tends to form a sludge in the hydrocarbons andunder conditions of, prolonged standing willsettle out to'form a slurry, in the-lower partof the'hydrocarbon, of highp lymer content. 7 y

Theinvention is more clearly.-illustrated by-the following descriptionwith reference to-thedraw ings, Fig. 1, Fig. 2 and Fig. 3 showing; various dlagramrnatic'flowv plans. I c c In View 0,1 the above considerations: there are 4 several possible methods of actually carrying out this process in practice. Fig. 1 consists of contacting the solutions in appropriate equipment such as turbo mixer I, packed tower, or in a mixing centrifugal pump, with the hydrocarbon immediately after the step in which the butadienefree solution-is heatedwin-lsoaken 1; under condi- -ti 0hs appropriatefor converting} the monomeric acetylenes to polymer. The cuprous salt solution is desorbed of butadiene in desorber 3, the butadienebeing removed through pipe 4. The buta l en-free'solut'ion passes through pipe 5 to soaker 2' where it is heated to polymerize the J acetylenes and passed through pipe 6 and cooler 1 topip:e-=8:- 011i is passed through pipe 8 and the twoyoiliandi essentially butadiene-free solution, passed to mixer l. The mixed solution and hydrocarbonare passed through pipe 9 to separator lflzirom. which the cuprous solution is withdrawn through pipe H and oili'with polymer in solution through?" pipel2. -Under these conditions-the polymeraare-larg ely: remoyedv as the dimers. and ccdimers since inv v actual practice, it "has. been found that the dime rs formed in. the solution? soaking.stage-have.-not: hadlsufiicient time-at high temperatures to polymerize much beyor'id the dimerstage... v Under such. conditions. the polymers are largely soluble in. hydrocarbon. solvent. The cscrubbing operation be conducted at temperatures. from:- atmospheric to; 2.00 Preferably, however; the temperatures should-be lee'pt aslow as.possibleinv ordertoretardfurther poly merizationofvthe. polymers dissolved-in the oil and-minimize theamount of- -sludge polymersv obtained-in.theoil-phase. y

Referring to Fig. 2, another methodfor carry: in out this process consists of injecting-- the hydrocarbon through pipe l3 into; the: buta-dienee free solution a s :it.passes-.throug;h. pipe Sandcim eulating-this; oil. therefrom,- through; the; soak-en? in; which? the solution: is heated to convert the monomeric? acetylenes. to polyr ners; -.The.- mixture of. oil. and; polymer is then passed. through pipe I5.4-,; cooler l15 toseparator 10'. The oil is then separated under gravity irom thecopper solution and maybe returned tothesolution soaking stage 2 with. some discard toprevent undue accumulae tiono f polymers in the oil; through-pipes, l-Z and l3= together withsomefreshoil: I U a The-resulting solution (and/ or suspension),- 01' polymers in the-hydrocarbon solvent may be treated in a number of-waysafter separation fromathe-z copper solution. a In onemethod "of operatic the hydrocarbon co ntaining-.-poi-ymer is simply d scarded or burned. after the' polymer-s hayeliaccumulatedin the added hydrocarbon; to the-extent of- 5 5o%. In-othercases-it may be desirablefto; remove part of the hydrocarbon solvent 'bydistillation' overhead, from! the'ipolymers. This operation" may be carried outin the presence of a flu'x'= oil of higher boiling point than the original solvent. For"' instance, n casebenzene is usedto' scrubthe solution, the solution of polymers-inbenzene may be fed to a fra'ctionatin'g column into the bottorn'of which 'aheavy OilfSillCIl as a gasoilis, continuously fed. The benzeneis tia lgen overhead leaving the polymers in"the oil which.,.can, subsequently be fed to. a I burning groundnorto a furnace. In certain cases. it, is desirable-to add-to the solvent. an anti-oxidant inhibitor such. as phenols, polyhydric aromatics, aromatic. amines and, amino phenols. The. purpose of thesecompoundsis to retard. polymeriza e- -t.ion.-t.o insoluble. polymers; and: toprevent 8 0611:-

mulation of peroxides in the polymers as a resul of contact with air. 1

EXAMPLE In equipment shown in Fig. 3 a 72-hour run was conducted in which a copper solution was contacted with a C4 cut containing 75% butadiene and 2 70 acetylenes, these acetylenes being an equimolar mixture of vinyl and ethyl acetylene. The ratio of solution and hydrocarbon feed rates were such that the solution picked up 0.02 moi/liter (1.0 gram/liter) of acetylene per cycle through the system. After boiling off the butadiene in the desorption zone the solution was heated in the soaker for about 40 minutes thereby polymerizing 0.0199 mol of acetylene per liter of solution per pass. The solution leaving the soaker was scrubbed with xylene in a packed tower and the solution continually returned to the absorption system. This operation was continued for 72 hours and the solution tested at various times for its polymer content after leaving the zone in which it was scrubbed with xylene.

The C4 cut was passed through pipe to pipe 2| and absorber 22, the butadieneand acetylenefree gas being removed from absorber 22 by pipe 23. A cuprous solution introduced into absorber 22 through pipe 4| passed in countercurrent'fiow to the C4 cut. The cuprous solution containing dissolved butadiene and acetylenes passed from absorber 22 by pipe 40 to stripper 24 where it was heated to 80 F. by heating means not shown. The heated cuprous solution was passed through pipe 25 to desorber '28 where it was heated further to 145 F. The cuprous solution was then passed through pipe 21 by means of pump 28 tosoaker 29 maintained at 180 F. Make-up ammonia was added through pipe 30 to desorber 25. The cuprous solution was then passed through pipe 3| and cooler 32 to scrubber 33 where it was scrubbed with xylene. Tower 33 was simply a packed tower filled with xylene introduced through pipe 42 through which the solution flowed. The cuprous solution with some entrained xylene passed through pipe 38 through separator 36 to the top of absorber 22. Separator 3B allowed the xylene to separate from the cuprous solution, the xylene containing polymer being discarded through line 31. The purified butadiene boiled out of the solution in desorber 26 was passed completely or in part to stripper 24 via line 34 or recovered in part as product from line 35. The xylene in scrubber 33 when the polymer in solution has increased to was removed through pipe 43, the polymer separated and the xylene returned through pipe 42. The followingfigures show that all times during the operation the copper solution remained substantially free of polymeric material.

Throughout the entire run no solid polymers accumulated in the desorption, adsorption, and soaking solutions of the system. Some sludging of polymers in the wash xylene was observed. This sludging was of such a nature that the polymers were concentrated in the lower portion of the solvent and this portion could be withdrawn and discarded continuously.

It is not intended that this invention should be limited as regards the type of copper solution to which it is applied. Solutions of a wide range of composition may be used so long as they are effective for concentrating diolefins. The solutions may be either acid or basic in nature and may contain as a solubilizing agent such compounds as ammonia, methyl amine, dimethyl amine, pyridine, and other amino compounds.

I claim:

1. An improved copper ammonium acetate absorption and purification method for separating butadiene from a hydrocarbon mixture containing it, together with butenes and small amounts of acetylenes, comprising the steps of contact said mixture with a solution of copper ammonium acetate to obtain a rich solution containing butadiene and acetylenes, subsequently heating said rich solution to desorb butadiene whereby a lean solution substantially free of butadiene is obtained, exposing said lean solution to conditions causing polymerization of acetylenes, and washing said exposed solution with liquid butene.

2. The improvement in a process of using a solvent to separate a diolefin from a, mixture of saturated and unsaturated hydrocarbons containing a diolefin and acetylenes, which comprises contacting said mixture with a cuprous salt solution which selectively dissolves diolefin and acetylenes, separating the resulting cuprous salt solution with the dissolved diolefins and acetylenes from undissolved hydrocarbons, heating the cuprous salt solution with the diolefin and acetylenes in solution to dissolve the diolefin. then further heating the cuprous salt solution to polymerize cuprous salt solution by means of a hydrocarbon the acetylenes remaining in solution, and extracting resulting acetylene polymers from the solvent for the polymers, which solvent is immiscible with the cuprous salt solution.

3. The process according to claim 2, in which the cuprous salt solution of the diolefin and acetylenes is an aqueous solution of copper ammonium acetate containing butadiene and ethyl acetylenes, and in which the cuprous salt solution is returned to the contacting step.

CHARLES E. MORREIL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS .Number Name Date 2,318,988 Craig May 11, 1943 2,463,846 Bain et a1 Mar. 8. 1949 

1. AN IMPROVED COPPER AMMONIUM ACETATE ABSORPTION AND PURIFICATION METHOD FOR SEPARATING BUTADIENE FROM A HYDROCARBON MIXTURE CONTAINING IT, TOGETHER WITH BUTENES AND SMALL AMOUNTS OF ACETYLENES, COMPRISING THE STEPS OF CONTACTING SAID MIXTURE WITH A SOLUTION CONTAINING BUTAACETATE TO OBTAIN A RICH SOLUTION CONTAINING BUTADIENE AND ACETYLENES, SUBSEQUENTLY HEATING SAID RICH SOLUTION TO DESORB BUTADIENE IS OBSOLUTION SUBSEQUENTLY FREE OF BUTADIENE IS OBTAINED, EXPOSING SAID LEAN SOLUTION TO CONDITIONS CAUSING POLYMERIZATION OF ACETYLENES, AND WASHING SAID EXPOSED SOLUTION WITH LIQUID BUTENE. 